﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;

namespace NativeCode.Core.Data.LinqKit
{
	/// <summary>
	/// See http://www.albahari.com/expressions for information and examples.
	/// </summary>
	public static class PredicateBuilder
	{
		public static Expression<Func<T, bool>> True<T>()
		{
			return f => true;
		}

		public static Expression<Func<T, bool>> False<T>()
		{
			return f => false;
		}

		public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> right, Expression<Func<T, bool>> left)
		{
			InvocationExpression invocationExpression = Expression.Invoke(left, right.Parameters.Cast<Expression>());
			return Expression.Lambda<Func<T, bool>>(Expression.AndAlso(right.Body, invocationExpression), right.Parameters);
		}

		public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> right, Expression<Func<T, bool>> left)
		{
			InvocationExpression invocationExpression = Expression.Invoke(left, right.Parameters.Cast<Expression>());
			return Expression.Lambda<Func<T, bool>>(Expression.OrElse(right.Body, invocationExpression), right.Parameters);
		}

		public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
		{
			// build parameter map (from parameters of second to parameters of first)
			Dictionary<ParameterExpression, ParameterExpression> map = first.Parameters.Select((f, i) => new {f, s = second.Parameters[i]}).ToDictionary(p => p.s, p => p.f);

			// replace parameters in the second lambda expression with parameters from the first
			Expression secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);

			// apply composition of lambda expression bodies to parameters from the first expression 
			return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
		}

		public static Expression<Func<T, bool>> ComposeAnd<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
		{
			return first.Compose(second, Expression.And);
		}

		public static Expression<Func<T, bool>> ComposeOr<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
		{
			return first.Compose(second, Expression.Or);
		}

		#region Nested type: ParameterRebinder

		public class ParameterRebinder : ExpressionVisitor
		{
			private readonly Dictionary<ParameterExpression, ParameterExpression> _map;

			public ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
			{
				_map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
			}

			public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)
			{
				return new ParameterRebinder(map).Visit(exp);
			}

			protected override Expression VisitParameter(ParameterExpression p)
			{
				ParameterExpression replacement;
				if (_map.TryGetValue(p, out replacement))
				{
					p = replacement;
				}
				return base.VisitParameter(p);
			}
		}

		#endregion
	}
}